You are still using way too broad of a brush. The USA is broken down into States and then counties and then cities. They all differ in their laws governing defense and use of force. Some places you have a duty to retreat, others you can stand your ground, some places you can defend your castle but must retreat when not in your castle... In every case, there are extenuating circumstances that make each and every case unique.I only know that in the USA the law says you can defend yourself.
I know a guy (doesn't everyone) who has a concealed carry permit issued by the State of CA. (that is an accomplishment by itself...) While in San Francisco a number of years ago, he was in a parking garage where two guys pulled knives on him. He pulled his gun, they ran. When he reported it to the police, they were not at all interested in the two guys who pulled the knives. They were however very interested in why he had a gun at all. Had he not had quick access to a good lawyer, he would have spent the night (or more) in jail, as they were very interested in charging him. He legally carried, legally used and legally reported the incident and still needed a lawyer in order to go home.
The only blanket statement you should be making about what you can and can't do, in regard to use of force, is to learn and know the laws where you are... and have an attorney's number to call. Telling people you can do this or that, without understanding the specific laws in force, for where that person is... can lead to lots of legal problems.